The reason there is no siphon during cool-down is due to a breach in the closed system. A closed system requires no outside air to enter the system. Breaches are caused by various faults, including split hose ends, deformed cap gasket, hose cracks, loose clamps, radiator fractures, etc.

If air enters the cooling system, the siphon will be negated.

Pressure generated by a ruptured head gasket allowing exhaust gases into the cooling system, will, also, prevent a siphon from occurring.

 

That makes sense, thanks. I guess next step is pressure test on cooling system

 

89 Corvette only has a digital coolant temp gauge, no analog...WW

 

Yep - and check with NAPA that you were sold the correct cap. It's NOT likely your problem but it's where you were last so "confirm". That's a very good source for quality auto parts.

 

Still trying to gain information

If coolant is being pushed out and not sucked back in, is there a chance that's two different problems? The reason I'm asking is because I'm trying to determine if I have a leak in bottom of radiator. Could a leak on bottom of radiator cause both symptoms? As quick as I lose coolant I would expect to see the leak or white smoke in exhaust. None of this makes sense YET. Still not sure if I'm losing coolant from leak or just being pushed out into reserve tank Another question is if I take cap off radiator, start engine, should coolant start coming out of opening where cap was? Seems like I should see it flowing but not coming out. Sorry for all the questions, but I don't want to tear into engine until I am certain as I can be what the problem is. I have to wait until next week to rent pressure tester. I'm still not sure I don't just have air lock in system

If it is a blown head gasket, do most blow near back or front of head?

 

Most will loan you the tester for a deposit. They may not charge if you do the test there. With a small leak it might evaporate before you see it. And need to get all the air out. Fill it up and jack up the car to make it the high point.

 

mim0, be aware that the pressure tester that fits on the radiator only tests for pressure/leaks in the radiator. It does not test for block leaks.

If exhaust gases are entering the cooling system due to a ruptured head gasket, depending on the size of the rupture, you should see coolant and bubbles being being expelled through the radiator fill hole (cap off), or into the reservoir (cap on), and a rapid rise in temp.

The only visible coolant would be in the rapid filling of the reservoir caused by exhaust gases entering the system, if that is the problem.

Google Pressure Testing, and you will be provided with numerous methods.

 

Can happen anywhere.

 

I've been informed by Stant that all pressure caps are made for both 'open' and 'closed' cooling systems now (last 10 years +/-). This was not so 10 years ago.

 

It sounds like you just lost the syphon back to the radiator. Check the hose to the over flow bottle and also check the nipple at the reservoir tank to make sure there are no air leaks. If there are any air leaks as the fluid gets hot it will go to the over flow bottle and as it cools down it will not return to the reservoir tank. Good luck!

 

I wondering if I am reading my symptons all wrong and making more of it then it really is,,, I hope

here is the latest

the problem started not because it overheated, it never has, I just started getting low coolant light, on and off, mostly right after starting and driving a short distance

when I take off radiator cap, the coolant always look low, is this normal when engine is warm, I was thinking the coolant should always be near top even when warm or coolu
with cap off, if I open throttle, coolant level goes down, but then comes back up again..

If I but coolant in rad, put cap back on and check it after a short period to time, coolant is back down again, but not in overflow tank, temp is still good

when i run engine without cap on t-stat opens and I can see fluid moving. there are some bubbles, but I thought it is just from the fluid moving

replace low level sensor about a year ago because it kept coming on, and worked fine until now.

no steam in exhaust, oil looks good, there is some browning in rad fluid

I have put so much love and money into this car, it breaks my heart it has a problem and I am afraid to drive it

it doesnt bother me that much to fix or get fixed problem, what bothers me is not knowing what the problem is to get it fixed.

 

Start by pressure testing the radiator and block (both). Guessing doesn't help.

 

see above

 

This is actually pretty simple,

A leak of any kind in the cooling system will play Havoc with it's ability to recover Fluid from the Overflow/recovery tank.. or there is a High pressure leak at an head gasket, and this will also pressurize the cooling system and push coolant into the recovery tank.

As stated before do a pressure test, and see if, or not the system holds pressure. Also, Pick up a Block tester kit and see if there are exhaust gas's mixed in with your coolant. This is were you need to start, if you cannot visually spot a leak.

 

I will get back with results next week after the two tests are conducted

Thanks everyone

Mike

 

Mike, removing the t-stat, and capping the hole will allow pressurization of the rad and block.

If you have an oil cooler, that needs to be tested, also.

 

Never thought of oil cooler, thanks

Mike

 

Pull your spark plugs then pressurize your cooling system
In fact just look at the plugs esp 5 and 7 before doing anything

Sounds like the notorious 89 HG lets hope not

Pull your plugs first

 

Mike, a test liquid is available from AutoZone (OEM/Block tester test fluid - $9) that will show if exhaust gases are present in the coolant. Recommend you try this test first.

 

edit:
i see above that Seabright had noted the siphoning issue. right on. you may well have a slightly blown head gasket. mine turned out to be quite small. but make sure you check the cap/hose/neck as well!






MLM0, I just went through all of this on my 85.
Just putting it all back together with a new headgasket.


Red had the first thing to check and im only repeating it because i don't think i saw that you reported it passed inspection.

your rad fluid expands when it gets hot and pressurized.

the pressure overcomes the spring in the cap, and opens up access to the overflow hose to the overflow tank.

in other words just because fluid keeps going to your overflow tank, it doesn't neccessitate the requirement that its exhaust gasses/blown hg that is forcing the fluid out. hopefully not.

anyway, when you turn the car off, the system cools off, and it SHOULD "vacuum" the fluid sitting in your overflow tank back into the rad. Its a closed system.

If it is NOT doing this, sounds like its not, then the very first thing to check, is your cap, and your overflow hose and a crack on the neck of your rad (if its plastic) right at the cap. in other words, if the system is drawing in air somewhere instead of drawing the fluid back up the overflow hose, this is yoru problem.

honestly its probably your problem.



i say that because i know it is what my 85's problem STARTED OUT AS.

but, remember, each time your get the expansion, which gets hotter each time because you have less coolant each time you run the engine, and none of it is coming back in, then this leads to a condition where you have not enough coolant and boom you overheat and blow a head gasket. I am about 95% sure this is how it happend to my 85.

When i was in the stage of the process like you are, diagnosing, I found that the EXACT same thing happening. i would fill, burp (by lifting the front end, and even better if you can lift the passenger side up even higher) and following the L98 burp procedure....even when doing that...i would have the coolant fill my overflow reservoir, i simply checked it a few times while it warmed up and i could see it filling itself.

But then when i shut if off and it cooled down, it never sucked it back in.

i also own an 87. i went over and grabbed the 87's rad cap.

put it on, and low and behold, it started to suck the fluid back in. there are two seals on the caps. in my case, the seal that seals against the top lip of the rad was old and dry and cracked and it was letting air into the system when it was cooling/de-pressurizing. obviously air flows easyier than lifting that fluid.

However, my car still had a blown head gasket in #7. My guess is that the blown head gasket was caused by this issue, and it was just never recognized.

sorry so long, hope that helps.

also, you asked if a loose intake gasket could cause it. yes absolutely it could. remember your cooling system is supposed to be a sealed unit. pressure neither enters, or leaves. so if your intake manifold bolts are loose (this was also the case on my 85) then you will have a spot where the vacuum can occur.

i am new to all of this, but im just sharing what i found with my 85.

im am willing to bet that so much of the blown #7 head gaskets we have in these cars, is because of a cap seal not sealing good enough to let the rad system suck in the overflow fluid again. which is a negative feedback cycle as next time if fills it a bit more if it gets hot enough. and eventually the car runs with not enough coolant, and you get stuck in traffic on a hot day, and boom, it overheats because there isn't enough coolant circulating and the water pump is cavitating. all your fluid is the overflow.

if parts of what i have written are wrong, im sure they will be corrected.

in my case, with my 85, even after i fixed the cap, and cut the hose down a bit to get uncracked hose at the rad overflow nipple, when i pressureized my cylinder 7, my overflow tank bubbled. which meant that the pressurized air i was in jecting was going though the blown hg at #7, into the cooling system, overcame the 16psi pressure of the cap, and out the hose, into the overflow. on my long "seeping intake bolts" thread, its all documented and video's. but its really long.

ive learned way more about the systems that operate the car than i ever thought i would. or cared to. but hey. such is the life of owning a really old but amazingly cool car.